The present invention relates to a helical scanning type magnetic recording and reproducing apparatus for executing recording and reproducing operation by use of a magnetic tape wound around a part of a circumferential surface of a drum of an upper drum and a lower drum and a plurality of rotary magnetic heads. More specifically, this invention relates to a magnetic recording and reproducing apparatus for reproducing data from the magnetic tape under excellent conditions when the recorded magnetic tape is being moved at a travel speed different from that at which data are recorded.
The helical scanning type magnetic recording and reproducing apparatus for recording and reproducing data to and from a magnetic tape wound around a part of a circumferential surface of a drum of an upper drum and a lower drum by use of a plurality of rotary magnetic heads has been so far well known and widely used as a VTR. In addition, this recording and reproducing apparatus has now been unitized as an apparatus of a large memory capacity which can record and reproduce a great amount of digital data.
In the helical scanning type magnetic recording and reproducing apparatus as described above, as a means for achieving high density recording, a pair of rotary magnetic heads having two magnetic gaps of two opposite azimuth angles are used. In more detail, one of the rotary magnetic heads has a magnetic gap whose azimuth angle is set at a predetermined angle less than 90 degrees in the clockwise direction with respect to the width direction of the recording traces (tracks). The other has a magnetic gap whose azimuth angle is set at a predetermined angle less than 90 degrees in the counterclockwise direction with respect to the width direction of the recording traces (tracks).
The two rotary magnetic heads are arranged at 180 degree symmetrical positions on the circumference of an upper drum and rotated at a predetermined number of rotations. Here, a magnetic tape is moved at a predetermined travel speed under such conditions that a reference edge position of the magnetic tape wound spirally around at least a part of the circumferential surfaces of the upper and lower drums is restricted by a guide portion (lead) formed at a lower drum. Data are recorded or reproduced to and from the magnetic tape when it is helically scanned by a pair of the rotary magnetic heads alternately in sequence. That is, data can be recorded on traces formed on the magnetic tape in sequence and in close vicinity to each other or the recorded data can be reproduced from the recorded traces, in correspondence to each 180-degree rotation of a pair of the two rotary magnetic heads.
Further, in the helical scanning type magnetic recording and reproducing apparatus, in order to record and reproduce wide band signals, a plurality of magnetic rotary heads having magnetic gaps of different azimuth angles are juxtaposed at two 180-degree symmetrical positions of the upper drum. A plurality of parallel arranged recorded traces can be formed at the same time by use of a plurality of the rotary magnetic heads which constitute a rotary magnetic head assembly.
Further, in the helical scanning type magnetic recording and reproducing apparatus, in the case where the wide band signal to be recorded and reproduced is an analog signal, the analog signal is extended on the time axis as a plurality of simultaneous signals. The extended simultaneous signals are recorded or reproduced in parallel to each other by the rotary magnetic heads. Further, in the case where recorded and reproduced signal is a wide-band digital signal of high bit rate, the digital signal is transformed into a plurality of digital signals of low bit rate and then the transformed digital signals are recorded or reproduced in parallel to each other by the rotary magnetic heads.
Now, in the above-mentioned helical scanning type magnetic recording and reproducing apparatus, the pattern of the recorded traces formed on the magnetic tape in accordance with the rotational locus of the rotary magnetic heads can be decided on the basis of various conditions such as the drum diameter, the number of rotations of the rotary magnetic heads, the rotational direction of the rotary magnetic heads, the travel speed of the magnetic tape, the travel direction of the magnetic tape, the track angle, the head track width, the recorded region width on the magnetic tape, etc. Therefore, when the conditions of the travel direction and the travel speed, for instance, of the magnetic tape change according to change of the operation mode of the magnetic recording and reproducing apparatus, the rotational locus pattern described on the magnetic tape by the rotary magnetic heads changes as shown in FIG. 1.
For instance, in the case where the magnetic recording and reproducing apparatus of VHS system (Trademark) is in SP mode, the rotary magnetic heads mounted on a rotary drum having a diameter of 62 mm are rotating at 1800 r.p.m. and the magnetic tape wound around a part of the outer circumferences of the upper rotary drum and a lower stationary drum is moved in the forward direction at a travel speed of 33.35 mm/sec in both the recording and reproducing operation. Under these conditions, the rotational locus of the rotary magnetic heads formed on the magnetic tape by the rotary magnetic heads is angled at 5.degree. 58' 9.9" with respect to the reference edge of the magnetic tape.
Further, in the magnetic recording and reproducing apparatus of VHS system, suppose that the rotary magnetic heads mounted on a rotary drum having a diameter of 62 mm are rotating at 1800 r.p.m. and the magnetic tape wound around a part of the outer circumferences of the drums is moved in the forward direction at a travel speed of 66.7 mm/sec in the reproducing operation (twice speed reproduction in the forward direction.) Under these conditions, the rotational locus of the rotary magnetic heads formed on the magnetic tape by the rotary magnetic heads is angled at 6.degree. 2' 19.2" with respect to the reference edge of the magnetic tape.
Further, in the magnetic recording and reproducing apparatus of VHS system, suppose that the rotary magnetic heads mounted on a upper rotary drum having a diameter of 62 mm are rotating at 1800 r.p.m. and the magnetic tape wound around a part of the outer circumferences of the upper rotary drum and a lower stationary drum is moved in the opposite direction at a travel speed of 66.7 mm/sec in the reproducing operation (twice speed reproduction in the reverse direction.) Under these conditions, the rotational locus of the rotary magnetic heads formed on the magnetic tape by the rotary magnetic heads is angled at 5.degree. 54' 6.2" with respect to the reference edge of the magnetic tape.
Further, in the magnetic recording and reproducing apparatus of VHS system, suppose that the rotary magnetic heads mounted on a upper rotary drum having a diameter of 62 mm are rotating at 1800 r.p.m. and the magnetic tape wound around a part of the outer circumferences of the upper rotary drum and a lower stationary drum is kept stopped. In this case, the rotational locus of the rotary magnetic heads formed on the magnetic tape by the rotary magnetic heads is angled at 5.degree. 56' 7.4" with respect to the reference edge of the magnetic tape.
Further, on condition that the inclination angle of a rotary axle of the rotary magnetic head does not change, the position of the rotational locus of the rotary magnetic heads described in the space is kept constant. That is, on condition that the magnetic tape is kept stopped, the rotational locus of the rotary magnetic head formed on the magnetic tape by the rotary magnetic head (i.e., the rotational locus of the rotary magnetic head in still reproduction) can be represented by a straight line connected between a start point and a zero point in FIG. 1.
In use of the magnetic recording and reproducing apparatus, in addition to the normal reproduction such that recorded data are reproduced at a tape travel speed the same as that in the recording operation, there are widely used a trick play such that recorded data are reproduced at a tape travel speed and in a tape travel direction different from those in the recording operation (including stop). In these reproduction modes, as apparent from the above-mentioned examples shown in FIG. 1, when the magnetic tape travel speed and direction change, the rotation locus of the rotary magnetic heads differs according to the different tape travel speed and direction, as shown in FIG. 1.
In FIG. 1, T denotes a magnetic tape; "a" denotes a travel direction of the rotary magnetic head; "b" denotes a travel direction of the magnetic tape T; and Tr, Tr, . . . , denote sequential recorded traces (tracks) formed on the magnetic tape T moving at a predetermined travel speed in the forward direction in accordance with the rotational locus of the rotary magnetic heads obliquely crossing the travel direction of the magnetic tape. Here, the recorded traces are in parallel to the straight line connected between the start point and a point x(+1) in FIG. 1.
The straight line connected between the start point and the 0 point shown in FIG. 1 indicates a rotational locus formed on the magnetic tape T by the rotary magnetic head rotating at a predetermined number of rotations in the "a" direction on condition that the magnetic tape T is kept stopped.
Further, the straight line connected between the start point and the point x(+1) shown in FIG. 1 indicates the rotational locus formed on the moving magnetic tape T by the rotating magnetic head, obtained when the travel direction "b" and speed of the magnetic tape are the same as those in the recording operation (for forming the recorded traces on the magnetic tape T) and further when the rotational direction and speed of the rotary magnetic head are also the same as those in the recording operation.
By the way, in the expression of x(+1), x(+2), x(+3), . . . , x(+n), x(-1), x(-2), x(-3), . . . , x(-n) shown in FIG. 1, "+" indicates that the magnetic tape is moved in the travel direction the same as that in recording operation; "-" indicates that the magnetic tape is moved in the travel direction opposite to that in recording operation; and 1, 2, 3, . . . , n indicate a multiple number of the magnetic tape travel speed when the magnetic tape travel speed in the recording operation is determined as one.
Further, in FIG. 1, a plurality of arrow straight lines extending from the start point in the radial directions indicate the rotational locus directions of the rotary magnetic heads formed on the moving magnetic tape, when the magnetic tape travel direction and speed are both changed to various values, on condition that the rotational direction and speed of the rotary magnetic heads are kept at the same values as in the recording operation.
Further, in the case of the FF reproduction such that the travel direction of the magnetic tape T is the same as that in the recording operation, the rotation locus direction formed on the moving magnetic head by the magnetic heads changes with increasing multiple number of the magnetic tape travel speed from a start point S in the clockwise direction FF in FIG. 2. Further, in the case of the FR reproduction such that the travel direction of the magnetic tape T is opposite to that in the recording operation, the rotation locus direction formed on the moving magnetic head by the magnetic heads changes with increasing multiple number of the magnetic tape travel speed from the start point S in the counterclockwise direction FR in FIG. 1.
As described above, when the magnetic tape travel speed in the reproduction operation is different from that in the recording operation, the rotational locus of the rotary magnetic heads crosses the recorded traces formed on the recorded magnetic tape in the reproduction operation. Therefore, when the reproduction operation is executed under such condition that the rotational locus of the rotary magnetic heads crosses the recorded traces formed on the recorded magnetic tape, it is apparent that the signals recorded on the recorded traces cannot be reproduced accurately by the rotary magnetic heads.
This problem can be solved by matching the rotational locus of the rotary magnetic heads with the recorded traces formed on the magnetic tape. Therefore, in the case of the VTR for recording and reproducing analog signals, various solving methods have been so far proposed as follows: (1) the rotary magnetic heads are mounted on an electricity-machine transducing element used as an actuator for an opened or closed loop control circuit, and the rotary magnetic heads are moved so as to follow the recorded traces on the magnetic tape; (2) the upper drum provided with the rotary magnetic heads is inclined together with the lower drum, to allow the rotary head to follow the recorded traces on the magnetic tape; (3) the height of the guide formed extending from the magnetic tape incoming side to the magnetic tape outgoing sides of the drum to restrict the width direction of the magnetic tape is changed, to allow the rotary heads to follow the recorded traces on the magnetic tape; and (4) the central axle of the drum is inclined and further the guide portion of the drum at the reference edge of the magnetic tape are both changed, to allow the rotary heads to follow the recorded traces on the magnetic tape.
In addition, in the VTR for recording and reproducing analog signals, the following solving method has been so far proposed: (5) in order to obtain relatively excellent reproduced signals by use of rotary magnetic heads having magnetic gaps of opposite azimuth angles, even when the magnetic tape is moved at a travel speed higher than that in the recording operation; that is, even when the rotational locus of the rotary magnetic heads used for the reproduction cross the recorded traces formed on the recorded magnetic tape, a double-azimuth head such that two magnetic heads having two magnetic gaps of two opposite azimuth angles are juxtaposed at two 180-degree symmetrical positions of the upper drum; the envelops of signals reproduced by the rotary magnetic heads are detected in reproduction operation, to select the reproduced signals generated by the rotary magnetic head for generating the reproduced signals of large signal level in sequence.
In the above-mentioned solving methods from (1) to (4), when the multiple number (or coefficient) of the tape travel speed is relatively small, these methods can be adopted relatively easily. However, when the travel speed of the magnetic tape in the reproduction operation is extremely higher than that in the recording operation, it is difficult to apply these methods.
Further, when the above-mentioned method (5) is applied to the VTR for recording and reproducing analog signals and further the multiple number of the tape travel speed is relatively small, relatively excellent results can be obtained. However, when the travel speed of the magnetic tape in the reproduction operation is selected to an extremely higher value than that in the recording operation, it is difficult to always obtain the excellent reproduction operation.
On the other hand, there is a case where signals are recorded and reproduced in the form of a bit stream of digital data and further that the reproduction operation of the apparatus is controlled on the basis of reproduced track data or control data included in the reproduced digital data bit stream. When the data are required to be reproduced at the magnetic tape travel speed extremely higher than that in the recording operation; that is, when the rotational locus of the rotary magnetic heads used in the reproduction operation cross the recorded traces formed on the recorded magnetic tape, it is impossible to accurately reproduce the track data and the control data included in the reproduced digital data bit stream, with the result that it is impossible to execute an accurate reproduction operation. In summary, since the above-mentioned solving methods (1) to (5) are not suitable for the ultra-high speed reproduction operation of digital signals, there exists a need of solving the above-mentioned problems.